Method and apparatus for calibrating geometrically an optical computer input system

ABSTRACT

A method and apparatus geometrically makes correction in an optical computer input system.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation patent application of U.S. patentapplication Ser. No. 08/342,905, filed Nov. 21, 1994, now abandoned,entitled "METHOD AND APPARATUS FOR CALIBRATING GEOMETRICALLY AN OPTICALCOMPUTER INPUT SYSTEM," which is a continuation patent application ofU.S. patent application Ser. No. 08/115,522, filed Aug. 31, 1993, nowabandoned, entitled "METHOD AND APPARATUS FOR CALIBRATING GEOMETRICALLYAN OPTICAL COMPUTER INPUT SYSTEM," which is a continuation patentapplication of U.S. patent application Ser. No. 07/656,803, filed Feb.14, 1991, now abandoned, entitled "METHOD AND APPARATUS FOR CALIBRATINGGEOMETRICALLY AN OPTICAL COMPUTER INPUT SYSTEM," which is acontinuation-in-part patent application of U.S. patent application Ser.No. 07/433,029, filed Nov. 7, 1989, now abandoned, entitled "COMPUTERINPUT SYSTEMS AND METHOD OF USING SAME", and of U.S. patent applicationSer. No. 07/611,416, filed Nov. 9, 1990, now U.S. Pat. No. 5,181,015,entitled "METHOD AND APPARATUS FOR CALIBRATING AN OPTICAL COMPUTER INPUTSYSTEM", each one of said applications being incorporated herein byreference as fully set forth herein.

TECHNICAL FIELD

The present invention relates in general to a method in apparatus forcalculating geometrically an optical computer input system. It moreparticularly relates to a system for calibrating geometrically fordistortion in connection with such an optical computer input system isshown and described in the said patent application.

BACKGROUND

A new optical computer input system is shown and described in saidparent patent application. Such system enable the use to shine a highintensity light onto a screen bearing a computer generated image toprovide auxiliary information for the computer. Such an input systemincludes an optical sensing device, such as a charged coupled devicecamera focused on to the screen. Thus the system can detect highintensity light images and discriminate them from the computer generatedimages, to input information interactively into the computer, in aconvenient manner, even in very low ambient light conditions.

While such a computer input system and method of using it has proven tobe highly satisfactory, it would be desirable to provide for a geometriccompensation or correction. There are various reasons why such ageometric correction is required. First, the screen onto which isprojected the computer generated image may not be a perfect rectangle aspresented to the sensing device or camera. In this regard, the screenmay be tilted either forward or backward, or from side to side, or anycombination thereof. Thus, the sensing device or camera will not trackproperly relative to the image visualized from the screen.

An even more significant problem is the problem of "keystoning" which iscaused by an overhead projector utilized in projecting the computergenerated image onto the screen. In this regard, the commonly knownkeystoning problem produces an image which has a longer top edge ascompared to its bottom edge. Such keystoning problem is well known withoverhead projectors, and thus, the sensing device or camera will producea distortion in sensing the image projected into the computer.

A third problem is caused by the improper alignment of a projectionpanel on the stage of the overhead projector. In this regard, if thepanel is not accurately aligned in a parallel manner on all sidesrelative to the projector's stage, the resulting image projected ontothe screen will also be askew.

A fourth problem relates to the project itself not being properlyaligned relative to the screen. Such is commonly the case where the neckportion of the overhead projector may be bent slightly due to excessiveuse or wear. This causes a result similar to the improper registrationof the panel on the stage of the projector.

A still further problem of geometric alignment is caused by the cameraor sensing device being tilted at an angle being tilted upwardly, ordownwardly, relative to the plane of the screen. The result is that adistortion may occur.

As a result of both described distortions due to the geometry of thescreen, projector and panel, as well as the camera itself, the camera isunable to accurately plot the various coordinates visualized from theimage projected on to the screen. As a result, tracking is not able tobe perfectly accomplished. Thus, when a light is projected onto thescreen, the camera may not accurately know the precise coordinates ofthe spot of light projected onto the screen. As a result, the computermay not accurately respond to the position of the light and incorrectdata can be entered. Thus, erroneous results might occur.

DISCLOSURE OF INVENTION

Therefore, the principle object of the present invention is to provide anew and improved geometric correction arrangement for an optical imagingsystem.

Briefly, the above referenced object is realized by providing a new andimproved geometric correction system.

There is provided in accordance with the present invention, a geometricsystem which includes an arrangement for generating geometricallycompensated relative coordinates for a projected image and for storingsuch coordinates.

Therefore, the system of the present invention produces a normalizationof the image of the screen to provide for the necessary correction.Thus, the resulting coordinates stored by the system are continuouslyused to adjust or convert the coordinates sensed by the camera. Thus,suitable corrections for the distorted are produced.

BRIEF DESCRIPTION OF DRAWINGS

The above mentioned and other objects and features of this invention,and the manner of attaining them will become apparent, and the inventionitself will be best understood by reference to the following descriptionof the embodiment of the invention in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a block diagram of the imaging system;

FIGS. 2 through 11 are diagrammatic views of various images or portionsof images helpful in understanding the operation of the presentinvention; and

FIGS. 12 through 17 are flow charts of computer software for the systemof FIG. 1 to illustrate the operation of the geometric correctionarrangement.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawings and more particularly FIG. 1 thereof,there is illustrated a computer input system 10 which modifies computergenerated images appearing on a screen 21, and which is constructed inaccordance with the present invention. The computer input system 10generally includes an image projection/detection system or arrangement11 whose input path (cable 17A) is coupled to the output of a video port17 of a computer 16. The arrangement 11 comprises a liquid crystal panel13 and a charge coupled device image sensor 14. The computer 16 is aconventional personal computer, such as a model PS/2 personal computermanufactured by International Business Machines. The computer 16includes a video monitor 19A and keyboard 19B. The panel 13 is driven bythe computer 16 for generating live images which are projected by anoverhead head projector 22 onto the screen 21.

The computer input system 10 also includes a signal processing unit 25coupled between the output path (cable 14A) of the image/detectionarrangement 11 and the input serial port 18 of the computer 16 via cable25A. The computer input system 10 further includes a light wand or lightgenerating pointing device 24, or a laser light generating device.

The projection/detection arrangement 11 detects the presence ofauxiliary light image or spot projected onto the viewing surface 21 bythe handheld/battery-operated light generating device 24, and generatesan analog electrical signal which is coupled to the signal processingunit 25 via cable 14A. The signal processing unit 25 responds to theanalog signal, and converts the signal into digital pixel coordinatesreference signals which identify the relative position of the auxiliarylight image on screen 21, which are transferred into the computer 16 viathe output cable 25A. Cable 25A is connected to the serial input port 18of the computer 16. Computer 16 responds to the pixel coordinatessignals and can alter its application program which causes the computergenerated image being projected onto the screen 21 to be modified. Forexample, the computer generated projected image on the viewing area 21can be modified in accordance with the information contained in thecoordinate references signals.

In the firmware stored in the signal processor 25 provides the necessarygeometric correction for the image in accordance with the presentinvention. As shown in FIG. 2, the correction commences by projecting abright rectangular light onto the screen to determine what correction isnecessary and then record the necessary information for converting thecoordinates to an adjusted relative coordinate. As shown on FIG. 2, atrue rectangular image is indicated at 80. It should be noted that eachone of the four sides of the image can be distorted in a generallyrectangular manner. On each side of the rectangular image 80 there aretwo possible triangular area of distortion possible. The arrangement ofthe present invention determines which one of the two triangular areasof distortion are present for each side of the rectangular image. Oncethat determination is made, a formula for the relative correction isgenerated and stored in the signal processor. Thus, there are eightpossible triangular areas of distortion indicated at 81 through 88.

In FIG. 3, there is shown an example of a grossly distorted rectangularimage 90 as an example. The first portion of the process or techniquefor doing the correction, is the actual corners of the projected imageare shown. The coordinates for the individual corners are shown in FIG.3. The technique for determining the corners are similar as shown anddescribed in the parent applications.

Once the corner coordinates are generated, a defined central coordinateof X , Y is located at the intersection of the diagonals of the cornersas indicated in FIG. 3. Thus, it is important to know for the purposesof the invention four quadrants of the generally rectangular image.

In this regard, if the coordinate identified on the screen is, forexample, in the upper left quadrant, then one of the two top trianglesmust be identified, together with one of the two left triangles. In sodoing, the relative coordinates for the identified spot of light on thescreen can be determined accordingly.

Referring now to FIGS. 12 through 17, the software for the geometricallycorrect arrangement will now be considered in greater detail Once arectangular image is projected onto the screen, such as the screen 21 ofFIG. 1, the software in the signal processor 25 determines thecoordinates of the four corners of the image appearing on the screen, asindicated at box 121 of FIG. 12. In this regard, the image sensor 14(FIG. 1) determines the interface between the bright image and theremaining portion of the screen, in a similar manner as described in theparent patent applications.

As indicated in box 122 in FIG. 12, and as shown in FIG. 3, thegeometric center of the screen is determined and defined at theintersection of diagonal lines extending through the corners. Andthereafter, as indicated in box 123, particular coordinates of a spot oflight projected onto the screen by the handheld light device 24 isdetermined. In this regard, a position X of the spot of light isdetermined to be either left of center or not. If it is determined to beleft of center, then the software will analyze whether the left edge isin perfect vertical alignment or whether it is distorted according toeither one or the other triangular areas of distortion 81 or 82, asindicated more clearly in FIGS. 4 and 5. As indicated in box 124, adetermination is made as to whether or not the left edge is a perfectlyaligned vertical edge. In this regard, the X coordinate of the top, leftcorner is compared with the X coordinate bottom, left corner. If theyare equal, then the edge is determined to be perfectly oriented in avertical disposition, and thus correction is not required. If suchoccurs, box 131 of FIG. 13 is entered.

Assuming that a left margin of the image is required to be corrected,the decision box 125 is entered as shown in FIG. 12 to determine whetherthe X coordinate of the top left corner is greater than the bottom leftcorner. This determination is made to learn whether there is rectangulardistortion area 81 (FIG. 4), or a triangular area of distortion shown at82 of FIG. 5. The triangular area 81 is in the shape of a right trianglehaving its based aligned with the bottom edge of the rectangular image.The rectangular area 82 is inverted from the area 81, and has its basecoextensive with the top edge of the rectangular image area.

At the decision box 125, if the X coordinate at the top left corner isgreater than the X coordinate at the bottom left corner then it isdetermined that a triangular image area 82 is present. In such asituation, the box 126 is entered and the left edge X coordinate iscalculated in the box 126. Thereafter, at the boxes 132, 133 theabsolute value of the X coordinate of the spot is calculated. This valueof the X coordinate is then used for sending to the computer 16, insteadof sending of the value of the X coordinate of the spot of light asdetected by the sensor 14. In this regard, the formula shown in theboxes 132 and 133 are used to scale the X coordinate of the spot oflight on the screen 21 to correct geometrically for any distortions. Itshould be understood that this X coordinate correction is calculated onthe slide for each spot of light detected by the image sensor 14.

Thus, it is to be understood that the initial storing of the X and Ycoordinates of the four corners and the defined center is the onlyinformation that need be saved during initialization process.Thereafter, the absolute values of the X and Y coordinates of the spotof light are calculated and supplied to the host computer 16 on the fly.

In order to determine the other left edge triangular area of distortionindicated at 81 at FIGS. 2 and 4, the decision box 125 of FIG. 12 willdetermine that the top left X coordinate is not greater than the bottomleft X coordinate, so that the box 126 is entered to calculate the leftedge X coordinate. After so calculating, the boxes 132 and 133 areentered to determine a different X ABSOLUTE value based upon thetriangular area 81 of distortion.

Referring again to box 123 to where the X coordinate position of thelight spot is determined to be left of center, if it is not left ofcenter then the decision box 141 of FIG. 14 is entered. A determinationwill then be made as to whether the right edge of the rectangular imagearea is perfectly vertical, or whether one of the two triangular areas83 and 84 at the right edge of the image area occurs. This operation issimilar to the operation of distinguishing the top triangular areas 81and 82.

At the decision box 141, there is determination made as to whether thetop right X coordinate is equal to the bottom right X coordinate. Ifthey are equal then box 145 is entered directly to determine if theright edge X coordinate is equal to the X coordinate of the top rightedge.

However, if they are not equal, then the box 142 is entered to determinewhether or not the top right X coordinate is greater than the bottomright X coordinate. If it is, then the right edge X coordinate iscalculated by the formula shown in box 143. Thereafter, as indicated bybox 151 and 152, the absolute value of the X coordinate is thencalculated knowing the right edge X coordinate and the X coordinate ofthe light spot and the X coordinate of the defined center. This absolutevalue of X is then used and supplied to the host computer 16.

Referring again to the decision box 142, if the top right X coordinateis not greater than the bottom right X coordinate, then the triangulararea 83 (FIG. 2) is identified and the box 144 is entered to calculatethe X coordinate of the right edge, thereafter, calculations are made atboxes 151 and 152 calculating the absolute value of the X coordinate.

Once the absolute value of the X coordinate is determined from eitherone or the two triangular areas 83 or 84, absolute value of the Ycoordinate is then calculated.

In order to calculate the relative value of the Y coordinate of thelight spot, the quadrant of the light spot is first determined at box153. In this regard, at box 153 a determination is made as to whether ornot the Y position of the spot is above the defined center. If it is,then the decision box 154 is entered to determine whether the top edgeis either horizontal or whether there are either one or two triangularareas 85 or 86 as shown in FIG. 2.

If a determination is made at box 154, if the top left Y coordinate isnot equal to the right Y coordinate, then at the decision box 155, adetermination is made as to whether or not the top left Y coordinate isless than the top right Y coordinate. This decision will identify whichone of the two top triangular areas 85 or 86 is present. If the decisionis positive, then the triangular area 86 is present. If the decision ispositive, then the triangular area 86 is identified and the calculationshown in box 156 is made to determine the top edge Y coordinate.Thereafter, as shown in box 163 (FIG. 16A), and box 164 of FIG. 16A, theabsolute value of Y is then determined for supplying it to the hostcomputer 16. This value of the absolute value of Y is a scaled value ofthe Y coordinate of the spot.

It the top triangular area 85 is present, a similar calculation is madeat box 161 for the top edge of the Y coordinate of the triangular area85. Thereafter, the absolute value of Y is then calculated boxes 163 and164.

Once the absolute value of the Y coordinate is calculated, a box 176 inFIG. 17 is entered to prepare and transmit to the host computer onceboth absolute value of the X coordinate and the absolute value of the Ycoordinates have been calculated. It should be noted that once theseabsolute values have been transmitted, the routine loops back to theinitial box 123 to repeat the cycle of operation for the next light spotdetected.

Referring again to box 153 of FIG. 15, if it is determined that the Yposition of the spot is not above the center, then the decision box 165of FIG. 16 is entered. A determination is then as to whether or not thebottom left Y coordinate is equal to the bottom right Y coordinate. Thepurpose of this determination is to decide whether the bottom edge ofthe rectangular viewing area is either horizontal, or at a triangularposition as indicated at either 87 or 88 in FIG. 2. If it is determinedthat the bottom edge is a true horizontal line, then the boxes 173through 175 are entered to calculate the value of the absolute value ofY as previously explained. On the other hand, if they are not equal,then the decision made in box 165 determines whether or not the bottomleft Y coordinate is greater than the bottom right Y coordinate. If itis, then the box 171 is entered to perform a calculation to determinethe bottom edge value of the Y coordinate. This calculation is based onthe triangular area 88, since the bottom left Y coordinate is greaterthan the bottom right Y coordinate. If the reverse is true, then thecalculation is made at box 172 based on the triangular area 87 todetermine the bottom edge Y coordinate. Thereafter, the absolute valueof the Y coordinate is calculated as previously described.

The following is a series of the equations used to perform the variouscalculations as illustrated in the flow charts to scale the X and Ycoordinates of the light spot.

1) FIRST DETERMINE X, Y POSITIONS OF EACH 4 CORNERS

2) NEXT TO FIND CENTER OF SCREEN, FIND INTERSECTION OF DIAGONAL LINES:

REFERRING TO FIG. 3, CALCULATE: ##EQU1## POINT SLOPE FORM OF EQUATION OFLINE

    y-Y.sub.BR =m.sub.LR (x-X.sub.BR)                          (3)

    y-Y.sub.BL =m.sub.RL (x-X.sub.BL)                          (4)

    y-Y.sub.BR =m.sub.LR x-m.sub.LR x.sub.BL                   (5)

    y-Y.sub.BL =m.sub.RL x-m.sub.RL X.sub.BL                   (6)

    y-m.sub.LR x=Y.sub.BR -m.sub.LR x.sub.BR                   (7)

    y-m.sub.RL x=Y.sub.BL -m.sub.RL X.sub.BL                   (8) ##EQU2## SUBSTITUTING INTO FIRST EQUATION

    y.sub.c =m.sub.LR X.sub.C -m.sub.LR X.sub.BR +Y.sub.BR     (12)

    Y.sub.C =m.sub.LR X.sub.C -m.sub.LR X.sub.BR +Y.sub.BR     (13)

3) DETERMINE IN WHICH QUADRANT, THE SPOT APPEARS BY APPLYING VERTICAL &HORIZONTAL CENTER LINES THROUGH THE CALCULATED CENTER.

4) COMPUTE THE ADJUSTED EDGE FOR BOTH X & Y IN THE FOUND QUANDRANT.##EQU3##

    SIDEOPP(ADJUSTMENT)=(DISTANCE)(TANα), WHERE DISTANCE EQUALS SIDE ADJ.(15)

REFERRING TO FIG. 4, FOR A LEFT EDGE OF ##EQU4##

    X.sub.RELATIVE =X.sub.RAW -X.sub.HOME NOTE: IF X.sub.REL IS NEGATIVE THEN POSITION IS OUTSIDE OF SCREEN.                            (17) ##EQU5## REFERRING TO FIG. 5, FOR A LEFT EDGE OF ##EQU6##

    X.sub.REL =X.sub.RAW -X.sub.HOME (NOTE: IF X.sub.REL IS NEGATIVE THEN POSITIVE IS OUTSIDE OF SCREEN                             (20) ##EQU7## REFERRING TO FIG. 6, FOR THE RIGHT EDGE OF ##EQU8##

    X.sub.REL =X.sub.RAW -X.sub.o (NOTE: IF X.sub.RAN >X.sub.RIGHT THEN OUTSIDE OF SCREEN)                                                (23) ##EQU9## REFERRING TO FIG. 7, FOR A RIGHT EDGE OF ##EQU10##

    X.sub.REL =X.sub.RAW -X.sub.C (NOTE: IF X.sub.RAW >X.sub.RIGHT THEN OUTSIDE OF SCREEN)                                                (26) ##EQU11## REFERRING TO FIG. 8, FOR A TOP EDGE OF ##EQU12##

    Y.sub.REL =Y.sub.RAW -Y.sub.HOME NOTE: IF Y.sub.RAW <Y.sub.HOME THEN OUTSIDE OF SCREEN)                                        (29) ##EQU13## REFERRING TO FIG. 9, FOR A TOP EDGE OF ##EQU14##

    Y.sub.REL =Y.sub.RAW -Y.sub.HOME ((NOTE: IF Y.sub.RAW <Y.sub.HOME THEN OUTSIDE OF SCREEN)                                        (32) ##EQU15## REFERRING TO FIG. 10, FOR A BOTTOM EDGE OF ##EQU16##

    Y.sub.REL =Y.sub.RAW -Y.sub.C (NOTE: IF Y.sub.RAW >Y.sub.BOTTOM THEN OUTSIDE OF SCREEN)                                        (35) ##EQU17## REFERRING TO FIG. 11, FOR A BOTTOM EDGE OF ##EQU18##

    Y.sub.REL =Y.sub.RAW -Y.sub.C (NOTE: IF Y.sub.RAW >Y.sub.BOTTOM THEN OUTSIDE OF SCREEN)                                        (38) ##EQU19##

While particular embodiments of the present invention have beendisclosed, it is to be understood that various different modificationsare possible and are contemplated within the true spirit and scope ofthe appended claims. There is no intention, therefore, of limitations tothe exact abstract or disclosure herein presented.

What is claimed is:
 1. A coordinate correction apparatuscomprising:image detection means for perceiving visually a displayedgenerally rectangularly shaped projected image having keystonedistortion; hand held auxiliary light means for successivelyilluminating the corners of the distorted image with spots of highintensity auxiliary control light for facilitating defining thegeometric form of the keystone distortion in the projected image; saidimage detection means responsive to said spots of high intensity lightonly during a calibration mode for generating a signal indicative of thelocation of the high intensity spots; signal processing means responsiveto said signal during said calibration mode for determining thegeometric center of the geometric form of the keystone distortiondefined by the intersection coordinate values of a pair of imaginarylines interconnecting the detected spots of high intensity light;distortion orientation calculating means responsive to the determinedgeometric center for determining quadrant scaling factors to facilitatedetermining corrected coordinate values for detected spots of highintensity auxiliary control light during a normal mode of operation;said signal processing means storing the scaling factors for use duringsaid normal mode of operation to enable said signal processing means toconvert subsequently a determined auxiliary light sensing coordinatevalue relative to another computer generated projected image havingsubstantially the same keystone distortion as said first mentionedprojected image; said signal processing means using said stored scalingfactors for converting the determined auxiliary light sensory coordinatevalues to absolute coordinate values, said absolute coordinate valuesbeing indicative of corresponding coordinate value information defininga fixed location within said another computer generated image.
 2. Anapparatus according to claim 1, further comprising:means for determiningthe corner x,y coordinate values for each respective corner of thedisplayed image; and means for determining the x,y coordinate values fora defined center within the displayed image area, wherein said imagearea is bounded by the four respective edges of the displayed image. 3.An apparatus according to claim 2, wherein said means for determiningthe x,y coordinate value for said defined center includes point slopedetermining means.
 4. An apparatus according to claim 3, wherein saidpoint slope determining means includes algorithm means.
 5. An apparatusaccording to claim 4, wherein said algorithm means includes means forsolving an equation: ##EQU20## wherein y_(TL) is indicative of adetermined Y top left coordinate value:wherein Y_(BR) is indicative of adetermined y bottom right coordinate value; wherein X_(TL) is indicativeof a determined X top left coordinate value; and wherein X_(BR) isindicative of a determined Y bottom right coordinate value.
 6. Anapparatus according to claim 5, wherein said algorithm means includesmeans for solving a pair of equations: ##EQU21##
 7. An apparatusaccording to claim 1 further comprising: means for determining the x,ycoordinate locations of each respective corner of the displayed image;andmeans for determining a defined center coordinate location for thedisplayed image.
 8. An apparatus according to claim 1, wherein saiddistortion orientation calculating means includes:means for calculatingan adjusted edge for both X and Y stored determined correctioncoordinate location values in the quadrant of the determined geometriccenter; and means for calculating an absolute x value and an absolute yvalue.
 9. An apparatus according to claim 8, wherein said absolute yvalue is: ##EQU22##10.
 10. An apparatus according to claim 9, whereinsaid Y_(relative) is:

    Y.sub.relative =Y.sub.SPOT -Y.sub.c.


11. An apparatus according to claim 10, wherein said y_(spot) isindicative of the y coordinate value of the projected x,y coordinateimage of light.
 12. An apparatus according to claim 8, wherein saidabsolute x value is ##EQU23##
 13. An apparatus according to claim 12,wherein said X_(RELATIVE) is:

    X.sub.relative =X.sub.SPOT -X.sub.left edge.


14. An apparatus according to claim 13, wherein said x_(SPOT) isindicative of the x coordinate image of light.
 15. An apparatusaccording to claim 14, wherein said X left edge is X_(TL).
 16. Anapparatus according to claim 13, wherein said X left edge is X_(TL). 17.An apparatus according to claim 1, further comprising:said imagedetection means responsive to the projected image in another calibrationmode for perceiving visually the distorted image and for generating avideo signal indicative of the projected image; said signal processingmeans further being responsive to said image detection means fordetermining image detection coordinate values for the distorted image,said distorted image having four determined corner coordinate values andassociated right, left, top and bottom boundaries; left boundarydistortion determination means for calculating whether or not the leftboundary is aligned vertically relative to its associated determinedcorner coordinate values; right boundary distortion determination meansfor calculating whether or not the right boundary is aligned verticallyrelative to its associated determined coordinate values; top boundarydistortion determination means for calculating whether or not the topboundary is aligned horizontally relative to its associated determinedcorner coordinate values; bottom boundary distortion determination meansfor calculating whether or not the bottom boundary is alignedhorizontally relative to its associated determined corner coordinatevalues; left distortion orientation means responsive to said leftboundary distortion determination means for determining whetherdetermined left boundary distortion is rectangular distortion ortriangular distortion; left triangular distortion correction means forcalculating a set of corrected image detection coordinate values for theleft edge of the distorted image; left rectangular distortion correctionmeans for calculating another set of corrected image detectioncoordinate values for the left edge of the distorted image; absolutecorrection means responsive to said left triangular distortioncorrection means and said left rectangular distortion correction meansfor converting one set of the left edge corrected image detectioncoordinate values to absolute computer coordinate values; rightdistortion orientation means responsive to said right boundarydistortion determination means for determining whether determined rightboundary distortion is rectangular distortion or triangular distortion;right triangular distortion correction means for calculating a set ofcorrected image detection coordinate values for the right edge of thedistorted image; right rectangular distortion correction means forcalculating another set of corrected image detection coordinate valuesfor the right edge of the distorted image; absolute correction meansresponsive to said right triangular distortion correction means and saidright rectangular distortion correction means for converting one set ofthe right edge corrected image detection coordinate values to absolutecomputer coordinate values; top distortion orientation means responsiveto said top boundary distortion determination means for determiningwhether determined top boundary distortion is rectangular distortion ortriangular distortion; top triangular distortion correction means forcalculating a set of corrected image detection coordinate values for thetop edge of the distorted image; top rectangular distortion correctionmeans for calculating another set of corrected image detectioncoordinate values for the top edge of the distorted image; absolutecorrection means responsive to said top triangular distortion correctionmeans and said top rectangular distortion correction means forconverting one set of the top edge corrected image detection coordinatevalues to absolute computer coordinate values; bottom distortionorientation means responsive to said bottom boundary distortiondetermination means for determining whether determined bottom boundarydistortion is rectangular distortion or triangular distortion; bottomtriangular distortion correction means for calculating a set ofcorrected image detection coordinate values for the bottom edge of thedistorted image; bottom rectangular distortion correction means forcalculating another set of corrected image detection coordinate valuesfor the bottom edge of the distorted image; absolute correction meansresponsive to said bottom triangular distortion correction means andsaid bottom rectangular distortion correction means for converting oneset of the bottom edge corrected image detection coordinate values toabsolute computer coordinate values; and whereby corrected coordinatevalues for the right, left, top and bottom boundaries are calculated tosubstantially eliminate errors in input coordinate information resultingfrom keystone image distortion in the projected image.
 18. An apparatusfor substantially eliminating errors in optical input informationresulting from image distortion in a projected image, comprisingmeansfor determining image detection coordinate values for any detectedsubstantially flat generally rectangularly shaped projected image havingpossible edge distortion, said distortion being a distortion caused by aheight differential between the position of the projected image on aviewing surface relative to the position of image projection meansproducing the projected image; said determined image detectioncoordinate values including four determined corner coordinate values;boundary distortion determination means for calculating whether or notany boundary between a pair of adjacent determined corner coordinatevalues is aligned rectilinearly relative to its associated determinedcorner coordinate values; distortion orientation means responsive tosaid boundary distortion determination means for determining theorientation of the distortion relative to an imaginary rectilinear lineforming part of an imaginary rectilinearly shaped image; distortioncorrection means for calculating a set of corrected image detectioncoordinate values to eliminate errors in coordinate informationresulting from edge distortion in the projected image; and absolutecorrection means responsive to said distortion correction means forconverting said set of corrected image detection coordinate values toabsolute coordinate values, said absolute coordinate values beingindicative of corresponding coordinate value information generated bysaid image projection means.